1. Field of the Invention
This invention relates to the art of forming traffic regulating signs or strips on roadway pavements and, more particularly, to providing a roadway pavement with traffic regulating and facilitating means such as traffic lanes dividing lines, roadway edge dividing lines and the like, by applying and securing on the roadway pavement surface a factory prefabricated tape material.
More specifically this invention concerns the art of forming traffic regulating signs and lines formed with prefabricated tape material the upper face of which is provided with retroreflective or retrocollimating elements capable of ensuring nighttime visibility at a safe visibility distance when the substantially sole source of light is provided by the headlamps of motor vehicles which travel along the road, that is a source of light the rays of which impinge on the tape surface at spots well in advance of the position of the vehicle, and travel in a direction which forms either a small or a very small angle with the generally planar surface of the roadway pavement and of the marking tape applied thereon.
2. Description of the Prior Art
This art is a well worked one and a wide patent literature describes several embodiments of this art. Various procedures, machines and compositions have been proposed for expediting the prefabrication of such tape materials and retroreflective means and applying and adhesively securing said material on and to a suitably prepared roadway pavement. The U.S. Pat. Nos. 3,587,415, 3,879,148 and 3,958,891 (corresponding to British patent specifications Nos. 1,245,834, 1,465,585 and 1,459,273), of the present applicant, are examples of such literature.
Traffic safety evidently depends on the above considered safety visibility distance at which brilliant spots provided by the retroreflectivity of individual retrocollimating elements can be clearly and unmistakeably seen by the vehicle's driver. The brilliancy of such spots depends on the efficiency of the retroreflecting means and is proportional to the effective cross-sectional area of the impinging and reflected beam of rays (that is the actual operatable impinged area). The amplitude of this area is therefore a most important factor.
Other means have been proposed and are currently produced and made use of for improving the visibility of roadway edge delineations at a distance. Such means, commonly indicated by the simple term "markers", consist of a sturdy generally metallic structure wherein one or more light reflective elements are accommodated and at least partially sheltered against traffic wear. Such markers are generally bulky and promote dangerous jerks in rapidly traveling vehicles which pass over them (such markers provide a valuable aid when delineating roadway edges, pedestrian crossings and the like, but they are undesirable say along highways and traffic lane dividing lines).
Such markers are costly, as to their manufacture and to their laying on and securing to the roadway pavement. Each marker is necessarily individually placed in its required location and requires working of the conglomerate or aggregate pavement composition. Even if mechanical tools can facilitate the operation, the securing of individual markers requires competent workmen and involves substantial labour.
On the other hand the provision of sharply bulging retroreflective elements comprising efficient light reflective components having a substantial reflective area exposed to grazing light impingement, is advantageous when considered from the sole point of view of nighttime visibility at a distance, and also in rainy weather, when a layer of water is formed upon the road surface and covers only slightly bulging retroreflective elements, preventing retrocollimation.